In the present Lok Sabha of India, a single party holds an absolute majority…

A single party winning an outright majority in the Lok Sabha — more than half of its 543 seats, i.e. at least 272 seats — entirely on its own, without needing any coalition ally, is a landmark event in India's parliamentary history, since long stretches of Indian politics have instead been dominated by coalition or externally-supported governments.

Applying this to the present (16th) Lok Sabha, elected in 2014:

1. In the 2014 general election, the Bharatiya Janata Party (BJP) won 282 seats on its own, crossing the majority mark of 272 without needing any coalition partner.

2. The last time before 2014 that a single party had achieved this feat was in the 1984 general election, when the Indian National Congress won 404 seats on its own under Rajiv Gandhi's leadership.

3. Between 1989 and 2009 (seven general elections in that stretch — 1989, 1991, 1996, 1998, 1999, 2004, and 2009), every government formed at the Centre was a coalition or was backed by outside support, since no single party crossed the majority threshold alone in that period.

4. The span between the two single-party-majority years is therefore 2014 − 1984 = 30 years.

Cross-checking each offered interval against 2014:

Only the 30-year interval correctly lands on 1984, the last prior single-party-majority year, confirming the answer. (The Tripura PSC's official Sub Inspector Excise 2014 answer key also confirms 30 years as the correct answer.)